Scroll elements have long been produced in iron base and other alloys using various forms of sand casting. Because, for most applications, these castings must subsequently be extensively machined to very precise tolerances and must be free of injurious defects, it is desirable to minimize casting tolerances and sand related quality problems such as scabs, inclusions and blow-holes. These considerations have tended to favor the application of premium casting methods such as shell molding and lost foam casting. Less costly casting methods, such as various green sand techniques have often been used, but typically with only modest success owing to considerations related to tolerances and quality. For green sand casting, tolerances for the most important casting features, such as the involute of a scroll component, can be improved through the use of shell, cold-box or similar cores and through careful attention to the design of core prints. Additionally, by locating the prints in the same side of the mold as the green sand cast features, tolerances can be further improved. Unfortunately, some sand related quality problems tend to remain. In the case of ordinary low cost horizontally parted molds, well known principles of design of the gating system (runners, gates, sprue bases, chokes, tails, etc.), can address the root cause of many of these quality problems with some success. In the case of very low cost vertically parted molds, as produced on a Disamatic mold making machine, even the most carefully designed conventional gating systems have been less successful in avoiding the generation of loose sand and sand related quality defects.
In sand casting a scroll component, the narrow and deep space of the involute vanes are especially susceptible to entrapping foreign material such as loose sand that might be carried along with the molten metal. The orientation of the involute is a factor in this susceptibility. Involutes that have a horizontal axis function as quite efficient traps. This horizontal involute orientation is generally applied in connection with lower cost vertically parted molds, the same parting line orientation which is prone to the generation of loose sand. Rather than attempting to rely on conventional gating and filter cores, a preferable approach is to apply a novel design to the gating system which will generate less loose sand. Expressed in general terms, with conventional gating in a vertically parted mold, it is believed that there are three causes for the generation of loose sand, high velocities, abrupt changes in direction and turbulence. This invention constitutes a remedy which can address these causes as appropriate.